Reset CTL on Cisco Unified Personal Communicator (CUPC) 8

One of the new features of CUPC 8 (or CSF in general) is that it supports a lot of the UCM encryption and security features.
If you are hopping between different clusters (because you are an SE) you might run into troubles with this.
For example you might have connected to a secure cluster before and now your CTL (Certificate Trust List) does not match with the new cluster. Therefore CUPC Presence and chat will work but the Softphone component will not.
In this case the CTL needs to be deleted.
This can be done by delete the CTL file in the following directory:
C:\%USERPROFILE%\AppData\Cisco\Unified Communications\Client Services Framework\Security\sec\lsc0

Be aware, that the "AppData" part might be localized, e.g. "Anwendungsdaten" in German.