Well, as I said, it just uses the core language string for 'Clean Cache'.
If you want to change it (without screwing up the menu and stuff), you would have to change the cache cleaner php file so it uses a different string.
In the file administrator/modules/mod_cachecleaner/cachecleaner/helper.php, line 43:
... title="'.JText::_( 'Clean Cache' ).'" ...
Change that to something like:
... title="'.JText::_( 'Clean your cache' ).'" ...
Then in the Cache Cleaner language file add:
CLEAN YOUR CACHE=If you click on this link the cache of your website will be cleared. If you need contact me for more info about this feature...