Subnet scanning question?

You must have 3 dhcp servers or subnet pools set up for this to happen. If these are in isolated locations they should be set only to obtain the local subnet for the network to function. If it is all in one building it seems a pointless setup. If you are not in the same subnet as another machine, nothing will let you communicate with it. Your It department are either making a mess of their job, or are deliberatey preventing reliable networking, although this is a poor way to do that. Generally a single router can not issue more than one subnet.