1. A method of content delivery, comprising: having an entity establish an enterprise content delivery network (ECDN) behind an enterprise firewall, wherein the entity has a private namespace that is not resolvable through public Internet DNS, the private namespace having a set of enterprise domains associated therewith; building a list of one or more enterprise domains that are candidates for caching in the ECDN, wherein an enterprise domain that is a candidate for caching has associated therewith a set of one or more IP addresses associated with nearby content servers managed as part of an Internet content delivery network (ICDN); upon receipt of a query to a domain, the request generated by an end user behind the enterprise firewall, determining if the domain is on the list; if the domain is on the list, returning a response to the query identifying an ECDN virtual zone; and resolving the ECDN virtual zone to identify a given one of the one or more IP addresses.