What Is Cross Domain Tracking
Cross domain tracking is a problem any online marketer will face while trying to track goals with Google Analytics. It happens frequently and reduces our ability to really understand our best source of traffic.
Cross domain Tracking define
Cross domain tracking happens every time a marketer decide to use two or more domains in his strategy. A typical case is the use of an SEO optimized blog, hosted in one domain (www.myseoblog.com), that will get use to attract organic traffic, and a sales page hosted under a different domain (www.mysalespages.com) . Google analytics can use only the cookie created by the domain itself, and by default, each domain is separate from the other domains. Each domain exist on their own, and therefore, cannot share information (by default). So for google the seoblog is an entity, with his own cookie, and the sales pages another entity totally independent from the seo blog.
NOTE: I remove the end of this post since it was obsolete. Please see this new post to learn more about how to do cross domain tracking http://www.simpleanalytics.net/cross-domain-tracking/