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We have two subdomains that have been verified in Google Webmaster Tools. These subdomains were used by 3rd parties which we no longer have an affiliation with (the subdomains no longer serve a purpose). We have been receiving an error message from Google: "Googlebot can't access your site. Over the last 24 hours, Googlebot encountered 1 errors while attempting to retrieve DNS information for your site. The overall error rate for DNS queries for your site is 100.00%".  I originally investigated using Webmaster Tools' URL Removal Tool to remove the subdomain, but there are no indexed pages. Is this a case of simply 'deleting' the site from the Manage Site tab in the Webmaster Tools interface?