Is it spelled out anywhere in Reg CC that an item drawn on a foreign institution is not elegible for conversion under Check 21? Or must we rely on the definitions of "bank" and "check" to make that distinction?

OSC AAA. 229.2(aaa) Substitute Check


3. Because a substitute check must be a representation of a check, a paper reproduction of something that is not a check cannot be a substitute check. For example, a savings bond or a check drawn on a non-U.S. branch of a foreign bank cannot be reconverted to a substitute check.