Search Engine Optimization

From A2Wiki

To minimize search engine results for a subdomain, you need to publicize the URLs that you do want to have indexed and try to reduce or eliminate any references to the subdomain.

You could also look into putting some Rewrite rules into a .htaccess file in your web root that will redirect any incoming requests to the undesired URL with the preferred URL, sending a 301 "Permanent move" code to the requester. This link (http://www.google.com/search?q=mod_rewrite+301+.htaccess) should help you find some examples.