> Adserver.com checks cookie from adserver.shoes.com 1. This is not possible from server-side. The way cookies work, cookies set by adserver.shoes.com are only

> Adserver.com checks cookie from adserver.shoes.com 1. This is not possible from server-side. The way cookies work, cookies set by adserver.shoes.com are only visible from documents hosted on *.shoes.com domains. And if the tracking is done client-side, by image, iframe or some other remote call, then this is trivially detected and blocked by adblocker. 2. How did "adserver.com" knew to check for "adserver.shoes.com" cookies? there might be hunderds clients, and trying to load cookies from every domain (adserver.shoes.com, adserver.computers.com, adserver.travel-to-india.com and so on) will take way too long.