Blocking unwanted domains

NT 4.0 domain (win2K thru win95 users)
because some VPN connections and laptops used on other domains in our domain, we occasionally see in unwelcome domains in the Entire Domains list. these are like: MSHome, RedDog, HomDom.
How do I:
1) locate the machine(s) responsible for advertizing these domains
2) block these domains from being visable on our network

Thanks
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Richard