Getting Pages removed from Google permanently
When a website is updated / revamped or completely rebuilt, it is important to tell Google what happens to those old URLs that you are no longer going to use.
Usually you have a choice of a 301 redirect (if this is possible) or a 404 “this page is no longer here” message with links back to the home page or the “new” page that replaced it. However it appears with 404 messages, that Google still comes back and indexes this page, therefore it has been suggested recently that the 410 message is now sending out a much clearer message, and that the Google Bot is listening.
So (for now), if you don’t want an old page to appear any more in Google, give the 410 message a try.