From LedHed's Wiki
Overview
Active Directory computer objects only update their group membership upon reboot (much like user objects update their membership at logon). Sometimes you need a computer to update its membership but can't reboot because the computer is serving some critical function.
KLIST
You can use c:\windows\system32\klist.exe and gpupdate.exe to force a refresh. klist.exe needs to be run with Domain Admin or higher privilege. It may even need to be run as the NT Authority\System account.
klist.exe /purge gpupdate /force
Reference
https://technet.microsoft.com/en-us/library/hh134826(v=ws.11).aspx