— to exclude the chametz of an Israelite in the domain of a gentile. Even though he (the Jew) can burn it, it is not in his domain; and to exclude the chametz of a gentile in the domain of a Jew, and chametz on which debris has fallen. Even though it is in his domain, he cannot burn it.
Chametz You Cannot Reach Does Not Violate the Prohibition
Mekhilta Tractate Pischa 17:17