To force Active Directory replication, on the server which needs forced to update, run using elevated CMD:
repadmin /syncall /AeD
A = All Partitions
e = Cross Site (Enterprise)
D = Show server name in output.
This will initiate a pull replication.
OR if you are already on on your main DC, and need to update any other servers in the AD, you can do a push replication:
repadmin /syncall /APeD
A = All Partitions
e = Cross Site (Enterprise)
D = Show server name in output.
P = Push
The technet article with further info can be found here:
https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/cc770963(v=ws.11)
Perhaps, you like me are trying to move away from the old CMD comandlines, and migrate into PowerShell – if that is the case, bad news -currently there is no update alternative for repadmin in powershell – the Get-ADReplication commands are great for troubleshooting but offer no easy interface for updating AD.