Page Cannot be Found - unknown page in Search Engine Index
Sometimes a page will come up in a search engine like Google, Bing, Yahoo, etc. that does not exist on your site. This is most common when you move your website to a new host as the new site may not have all the same web page url names. In order to tell the search engines about the new page - you should create a 301 redirect.
So how do you get rid of those old pages in the search engine index? It's not really in your control - but you can make a request to the individual search engine. For example - Google has a request tool for page removal whether the page exists or not.