If you are referring to the Safari cache, it's not possbile to empty the cache from the menu bar in the most recent version 6.
There is a workaround. From your Safari menu bar click Safari > Preferences then select the Advanced tab.
Click: Show Develop menu in menu bar
Now click Develop > Emtpy Caches
OR, from the menu bar click Safari > Reset Safari
Clearing the history will also empty the cache but unfortunately, it also deletes your History.
Here’s how to clean your caches:
1. Choose Users>your user name>Library>Caches.
2. From the Menu bar, choose Edit>Select All.
3. Drag all of the items to the Trash.
4. From the Macintosh HD, choose Library>Caches.
5. Choose Edit>Select All, and drag the items to the Trash. You’ll be required to type in an administrator’s password.
6. Restart your Mac.