First make sure you're looking in the correct place. The caching may be happening in windows itself or your application software rather than IIS. But it's possible IIS caches group membership the first time it's accessed, but I don't know myself, sorry. In the old days of classic asp you could do a quick edit on global.asa and that would force a reset of application variables. I doubt that helps you though
Bartender to Rene Descartes "have another beer?" Descartes: "I think not" and he vanished.