Set the Sync ID on the 'Master' layer you want to use (as you said)
then - turn on 'broadcast to remote Preview ON' in the catalyst control window on the desktop
On the remote servers, select playmode 'sync ID xx' where xx is the Sync ID you want to sync to on the 'Master' layers / server
If you don't turn on 'broadcast to remote Preview ON' it will only work on the same between layers on the same server. By enabling broadcast to remote Preview, information is broadcast over the network.
Also ensure that your Macs are within the same IP network address range and subnet
Simon