Looking for a bit of help on removing a no longer existing subdomain. Our hosting company setup a default "ftp" subdomain which basically pointed to the same address as our "www" domain. Somehow, Googlebot got ahold of this. We removed the subdomain about a year ago. However, pages from this subdomain still show up in the results. They are supplemental. I would like to figure how to get rid of these. My understanding is that Googlebot will only respect a 404 or 410. However, with the domain gone, Googlebot is receiving a DNS error.
How should I best deal with this? Should I recreate the subdomain and redirect everything to a 404? Not sure how to do this? Any clues or hints on what we should do?