Command/run prompt to clear cache?

[Cbomb]

All my games run fine single player, but whenever I join a multiplayer game in steam the game and steam both crash.

I had this same issue before and I saw someone mention a command/run prompt that fixed the issue but I cant find it again. It was after the windows 8.1 update. Think it cleaned the steam cache or something. Does that sound vaguely familiar to anyone?