It seems like the most common shortcut is `Ctrl + Shift + R`.

For Firefox:

* `Ctrl + F5` or `Ctrl + Shift + R` on Win XP, Win Vista, Win 7, Win 8 and Linux
* `command + shift + R` on OS X

For Chrome:

* `Ctrl+F5`, `Shift+F5`, `Ctrl+Shift-R` on Windows
* `Ctrll+Shift+R` on Linux
* `Command+Shift+R` on Mac

For IE:

* `CTRL+F5`

For Safari:

* http://en.wikipedia.org/wiki/Wikipedia:Bypass_your_cache#Safari

**References:**

https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly#os=winxp&browser=fx18
https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly#os=win7&browser=fx18
https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly#os=win8&browser=fx18
https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly#os=linux&browser=fx18
https://support.mozilla.org/en-US/kb/keyboard-shortcuts-perform-firefox-tasks-quickly#os=mac&browser=fx18

https://support.google.com/chrome/bin/answer.py?hl=en&answer=157179&topic=25799&rd=2