We accept Rabbi Shimon’s opinion[4] that chametz she’avar alav haPesach is a rabbinic injunction that prohibits eating or benefiting from chametz that was owned by a Jew on Pesach, due to the violation of bal yeira’eh ubal yimatzei.[5] When bal yeira’eh ubal yimatzei does not apply, neither does chametz she’avar alav haPesach.[6] Ostensibly, then, chametz that was included in bitul chametz,[7] which removes the Torah prohibition of bal yeira’eh ubal yimatzei,[8] should be permitted after Pesach. The Yerushalmi[9] cites a machloket regarding whether this is indeed the case. We accept the opinion of R. Yochanan, who forbids it due to concern that one will abuse the system.[10]
There would seem to be another factor that would incline us to be lenient in your case – you did not remember that you were in possession of the chametz in question. However, the Rambam[11] and Shulchan Aruch[12] rule that chametz she’avar alav haPesach is forbidden even when one left the chametz over b’shogeg (accidentally) or b’oness (due to extenuating circumstances). The Bi’ur Halacha[13] seriously considers the claim of some poskim that when the grounds for leniency can be combined (i.e., bitul was performed and the chametz was left accidentally), the prohibition of chametz she’avar alav haPesach does not apply. However, he focuses primarily on a case of oness, whereas your case is one of shogeg, which may be more severe.
Nevertheless, there is yet another important point of leniency here. Because you left Hong Kong more than thirty days before Pesach and did not have any intention to return until after Pesach, you were not required to perform bedikat chametz[14] before leaving.[15] There is a major machloket regarding whether this exemption applies only to the search for unknown chametz or whether one is exempt even from removing known chametz.[16] According to the lenient opinion, you did not neglect any responsibility, as someone in that situation may rely on the bitul he performs wherever he finds himself. If so, there certainly would not be a problem of chametz she’avar alav haPesach.
According to the opinion that you should have taken care of the chametz you knew about, when you were removing the chametz from your regular house, whether through a formal bedika or other means (including mechirat chametz), you should have sold the chametz in Hong Kong or had someone get rid of it.[17] Your failure to remember the Hong Kong chametz is not fundamentally different from doing a bedika but forgetting to look under the couch. Regarding a situation in which one performed an imperfect bedika and a proper bitul, the Mishna Berura[18] brings strong indications in both directions regarding whether chametz she’avar alav haPesach applies. He concludes that in the event of significant loss, one can sell the chametz to a non-Jew. This is usually forbidden for chametz she’avar alav haPesach, but it is permitted according to some opinions when one did bitul.
Bitul[19] and mechirat chametz[20] are effective only until an hour before chatzot (halachic midday) of the day before Pesach. Therefore, depending on where you live and at what time you did bitul on the night of the bedika, there could be a complication, as Hong Kong is between thirteen and sixteen hours ahead of the United States. (Mechirat chametz would definitely have had the complication unless there was an early sale.[21]) Although most poskim say that in such matters, we follow the owner’s place, not where the chametz is, the Igrot Moshe[22] asserts that if the chametz is in a location where the timing does not work out, it becomes forbidden.[23] However, given the other indications for leniency, we maintain that if the loss of an (expensive?) bottle of scotch is significant to you, you can sell it or give it as a present to a non-Jew.