Uhh, no that is exactly wrong. Clients are expected to ignore cookies that don't come from matching domains. If you request a resource from xxx.yyyy.com then the server that responds can set cookies for *.yyyy.com or xxx.yyyy.com but nothing else. What you are mixing in is the protection against you going to "http://www.xxx.com/" and that page calling a resource from "http://www.eviladplace.com/ad/tracker" and you picking up a cookie from a site you didn't even know you visited.

All the domain parameter is for is setting the depth into your own domain. That way a server at www.cs.xxx.edu can set one cookie for all *.xxx.edu and another at just *.cs.xxx.edu and one just for itself at www.cs.xxx.edu! If I could set cookies in the netscape.com domain for you from hostile.org you can be sure I would be... =)

LWP is most certainly the right answer tho! Look at HTTP::Request's perldocs specifically

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$you = new YOU;
honk() if $you->love(perl)