If you are seeing a number of clients at a site that is not local to the SUP returning "Detection State Unknown" open up the scanagent.log on one of those clients and see if there's and error 0x80072efd. In the log you should also see which WSUS server the client is attempting to contact and on what port number. If you installed WSUS in the manner described in the docs this should be port 8530 and 8531. Try to telnet from the client to the WSUS server using the address and port number listed. If you do not get a reply have your network team check the firewall settings to make sure that the client is allowed to connect to the WSUS over the listed port.