Multiple SEPM v12.1 installations and Licensing.

We are working on 4 isolated Windows domains and we want to manage antivirus updates separately on each.  So we are installing 4 SEPMs (v12.1) that are dedicated to each domain.  Each domain has around 30-40 client nodes.

Is one license with total number of clients for the 4 domains enough to cover all?

Or is it needed to have 4 individual separate licenses for each SEPM installation.

Thanks for the help.