Here's How - Validating Information on the Web
Cross referencing is done by a simple search technique you can try in Google.
Go to Google. In the search box, start with "link:", then add the domain name of the site you would like to cross reference.
For example, to find out who has linked to the Pacific Northwest Tree Octopus website enter the following:
All of the search results that appear will have a link to this website somewhere on their pages.