1. A method comprising: receiving, by a Web server over a communications network including the Internet, a request from a user client device to access content of a target domain, the request being addressed to a domain address of the target domain; identifying, by the Web server, a new content domain that is determined to be relevant to the request to access content of a target domain based on a combination of the domain address of the target domain, source context factors that characterize the user client device, and historical relevance data associated with the target domain, the historical relevance data including source context factors of multiple users who requested to access at least one given address from addresses belonging to the domain address of the target domain and interests of the multiple users, the interests of the multiple users based on pre-access behavior of the multiple users; and providing, by the Web server, the user client device with access to content of the identified new content domain over the communications network, responsive to the request.