You just cannot wildcard it! So while -domain=>'.222.214.171.124' is invalid, -domain=>'2126.96.36.199' is not
(get rid of the period before the first set of numbers).
This has got to be allowed for one reason: what of servers that are located on a machine without a domain?
You have to be able to set cookies somehow!
Also, the only way to specify "subdomains" of an IP address is through port numbers.
It is apparently possible using HTTP::Cookie or the Set-Cookie2 header, but I have been unable to restrict a cookie to a specific port :(