Not to be outdone by the postal service, Google has introduced a highly requested feature that allows website owners to inform Google when they have moved to a new domain name. The “change of address” tool updates Google’s index to reflect your new URL. The changes last 180 days during which time the complete re-indexing will be completed.
Google requires website owners to be verified before they can report a domain move. Methods of verification include adding a meta tag to the home page of the site or uploading an HTML file to the server specifying some piece of information only Google would know, which they assure will not be used for anything else, due to their commitment to privacy.
Webmasters must make sure that both the old and new domains are verified before proceeding. Those who already use Google’s website tools are automatically verified. They also must ensure that their sites are not subdomains. Also, the change can only be made once per site. Google has not specified if there is a time limit on this.