It could be optional with a property; $findfile().cache - make the cache (doesn't make it by default) / or $findfile().nocache - don't make the cache (makes it by default.)

As for the cache being cleared after the current routine ends (re: qwerty) I think that kinda defeats the point of having it (ie not having to use the same subsequent $findfile calls.) I think it should just be reset with each $findfile call and maybe there could be a command added to clear it.