How Do I Clear Skype for Business/Lync Cache?

Skype for Business/Lync caches files locally on a PC or MAC to pull information quickly and efficiently. Common reasons you will want to clear Lync cache include:

• You can’t log in to Lync.
• Your Outlook and Lync integration is not functioning properly.
• You have issues with Presence.
• Your Contact list is out of date.
• You cannot search for users in Lync.

Skype for Business/Lync 2010 or 2013 for Windows

Lync 2011 for MAC

Skype for Business/Lync 2010 or 2013 for Windows

1. Log out of Lync.
2. Delete any sign-in info.
3. Exit Lync.
4. Open Run bar and type in %AppData%. Make sure you’re in the AppData directory and navigate to\Local\Microsoft\Office\15.0\Lync\ for Skype for Business and Lync 2013, or  \Local\Microsoft\Office\12.0\Lync\  for Lync 2010. 
5. Delete sip_profileName folder. If you do not see this folder, check the \Local\Microsoft\Communicator directory.
6. Delete all files in Tracing folder. Do not delete the folder itself.
7. Clear DNS cache: in Command Prompt run ipconfig /flushdns command.

Lync 2011 for MAC

1. Log out and quit Lync.
2. Go to Finder > press Command+Shift+G > type in /users/<MacUsername>/library > delete the following files:
   • Caches > com.microsoft.Lync
   • Internet Plug-Ins > MeetingJoinPlugin.plugin
   • Keychains > all files beginning with OC__KeyContainer
   • Logs > Microsoft-Lync-x.log and Microsoft-Lync.log
   • Preferences > com.microsoft.Lync.plist
   • Preferences > ByHost > MicrosoftLyncRegistrationDB.xxxx.plist
3. Go to Finder > press Command+Shift+G > type in /users/<MacUsername>/documents > navigate to Microsoft User Data > delete the following folders: Microsoft Lync Data and Microsoft Lync History.
4. Open Keychain Access from /Applications/Utilities folder.
5. Delete all keychains startting with OC__KeyContainer.
6. In your Login keychain, delete all e-mail address certificates.
7. Empty Trash.

Ref: https://kb.intermedia.net/Article/3238