title: how to track traffic across n domains with Google Analytics
body: <p>Example: I have 3 sites, a.com, b.com, and c.com. How can I keep track of the traffic that starts out at a.com and ends up at c.com, using Tag Manager and Universal Analytics?</p>
  
  <p>I know that using referral source is an easy enough thing to view in UA, but I really need referral referral source because UA only uses the most recent referrer, not a referrer <em>n</em> sites back.</p>
  
  <p>Please note that this question is not just about cross-domain tracking, rather keeping track of a site visited before the current referral.</p>