When your Tiki is acting up, clearing the server cache can be a good thing.
tiki-admin_system.php when logged in as an admin, there is a item labelled "Tiki Cache/Sys Admin" on the Settings part of the main Tiki menu, and one on the Quick Admin module (if enabled).
You can also clear the cache from the command line by doing
php console.php cache:clear
This is not the same thing as clearing browser cache