(ctrl-f5 on firefox)
It's shift in Windows, and option in OSX
My friend tried every control key in OSX, but none of them did a hard refresh. He had to clear his cache every time. (older version of OS X, though, so maybe it didn't understand it?)
<edit> from Wikipedia's editing page, "Mozilla / Firefox / Safari: hold Shift while clicking Reload, or press either Ctrl-F5 or Ctrl-R (Command-R on a Macintosh);" *shrug*