Hierarchical cache relations

The clients A-D have two levels of hierarchy, while client E has only one level of hierarchy, which means that if he sends a HTTP request, it goes directly to proxy A and proxies B-C are not involved at all. If one of the clients marked as A-D sends a HTTP request, it goes through the relevant proxy, and if there is a "cache miss" it sends a ICP request to the sibling proxy and the parent proxy.