Use to limit the domains for which a neighbor cache will be
	queried.

	Usage:
		cache_peer_domain cache-host domain [domain ...]
		cache_peer_domain cache-host !domain

	For example, specifying

		cache_peer_domain parent.foo.net	.edu

	has the effect such that UDP query packets are sent to
	'bigserver' only when the requested object exists on a
	server in the .edu domain.  Prefixing the domainname
	with '!' means the cache will be queried for objects
	NOT in that domain.

	NOTE:	* Any number of domains may be given for a cache-host,
		  either on the same or separate lines.
		* When multiple domains are given for a particular
		  cache-host, the first matched domain is applied.
		* Cache hosts with no domain restrictions are queried
		  for all requests.
		* There are no defaults.
		* There is also a 'cache_peer_access' tag in the ACL
		  section.