> There is no way the Fed can make them disappear.
There's no US precedent, but US government could do something like India's 2016 Demonitization: require new notes, exchange current notes for a limited time only, also limited per person. This might not completely wipe out foreign physical USD holdings, but it would probably make a dent; logistics alone for replacing all the bills would make a dent.
That said, I don't think there's any reason for the US government to do such a thing, and it would most likely lead to significantly lower confidence.