Multiple Domain Names = Multiple Page Ranks

[HardlyNoticable]

We often create websites that have more than one domain name. For instance, because we are Canadian, our customers often register .ca domains but also register .com domains for "global presence" and just to make sure we get all of those people who type .com by accident.

We usually do this by registering both domains and pointing them both to the same property. So if visitors visit either the .ca or the .com domain names, both will resolve to the same website.

THE PROBLEM IS we seem to get two different PageRanks for the website, one for each address. I can understand what's happening; some people are linking to the .ca and some people are linking to the .com, creating two different PageRanks.

I wish there was some way (maybe there is and you're going to tell me about it) where one could say to Google:
"THIS domain is my primary domain. You can exclude all listings for these secondary domains if you instead add their PageRank to my primary domain."

I've seen some people say that one should use a 301 redirect. I admit that does what I want a bit. It at least helps to make sure future links are not pointing to the non-primary domains and gives the search engines a clue when they are spidering the content (although I'm still not clear what google does when it finds a 301. Does it move the PageRank contribution to the new content?).

Anyway, I wonder if there are any SEO supremos out there who can tell me what to do in these situations?

[bradbox]

You can use Google Webmaster Tools to set a preferred domain in a situation such as this.

[HardlyNoticable]

I do not think you are correct. I tried that first; but it only lets you say whether your listings should always or never user the www. prefix.

I WOULD like a tool, almost exactly like this, for multiple domain names. But I don't think there is one.

[AussieWebmaster]

go for the 301 to the main domain and also do it for the www.domain.com to just domain.com and and do www.domain.com/index.html as well