Well, you wouldn't use wc.com, would you, it's not available.
But look at a server like CIT for example: It puts cit2.net at the end of it's server name. We can detect that, do a DNS lookup on that address and find that it's IP matches the server's IP (which it does in CIT's case).
If CIT hadn't hosted the server on the same IP as their website, then they could instead put server.cit2.net in their URL, which we can then verify in the same way as above. This still provides a 'proof of ownership' of the server, as only the server owner can make that DNS entry.
We could then provide a search field that lets you search by the domain names we've verified in this way.
Nobody else could ever have a server on your domain without you knowing (unless it was hacked, obviously). We could easily engineer the filter to prevent people doing things like cit.net.someotherwebsite.ru.