How to perform a hard refresh in current versions of Firefox, IE, Chrome and Safari for Windows and Mac OS X?

Safari on OS X

• Hold Shift while pressing the reload button

Chrome on OS X

• Press Shift+⌘+R
• Hold Shift, ⌘, or ^ (or any additional modifier keys) while pressing the reload button

In Safari and Chrome you can see if any resources were loaded from a local cache by checking for 304 Not Modified responses in the network tab of the web inspector.

http://en.wikipedia.org/wiki/Wikipedia:Bypass_your_cache has instructions for common browsers on different platforms.