Assuming you are talking about ePO 4.5, you can sort machines that do not communicate.
I do it the following way and you can adapt the server task below to your needs.
Actions: 1. Run Query
Query name: Managed Inactive Agents , Language: English
1.1 Apply Tag
1.2 Move Systems to Another Group
System Tree group: My Organization\Sync_Points\Domain X
Disable System Tree sorting on these systems
To get this to function as you wish, you will need to go in to the Queries section of ePO and duplicate a query that closely matches what you want to do and then change the criteria of the query to match exactly with what machines you want to enumerate. Then set up the schedule with which you want it to run.
Hope this helps.