Cookies store information about us and our surfing habits (and they are yummy). One of the secure things about a cookie is that you can only access it within the web site to which the cookie belongs.
So if you are visiting www.kinlane.com
I can put a cookie on your computer, but only I can access it. I own the domain www.kinlane.com
I just watched a movie on a famous band on Netflix
. After watching I went to Youtube
to look up more videos on this band.
Before I could watch my video on Youtube
, I had to watch an advertisement trying to sell me Netflix
It seems like we should have a "header" or part of a cookie that any domain can read. So youtube.com could query netflix.com on my computer and see if I'm a Netflix member, or at the very least see I just came from Netflix.
Just a thought.