Thanks for your quick replies. Sorry to be awkward, but can you point me to where it states that cards only affect the region they are played into? I've been looking through the rulebook to no avail!
I had planned to come back to this thread to back it up with the rules when I had more time. Now that I am looking, technically, nothing supports are interpretation. So I am going to have to plead that it is an ommission on the card.
All other Chaos cards affect the region they are played in. But all other Choas cards make reference to "this region" and so are very clear. The rules hint around this by saying you can be blocked from playing in a region if both spaces are occupied, that you pay to play cards to regions, but never come out directly and say the card only affects the region it is in.
You can sidestep it a bit and say that the Chaos card's cost affects your domination value against that region so each card is tied to that region. But that is a weak argument.
So I am going to appeal to common sense and say that 1) all other cards are specific to "this region" and so AP inadvertantly left off the text.
And 2) even if it was a world-wide effect and purposely worded that way, it is extremely undervlaued at 0-cost. How can you shut down the entire board's domination step (except for you) by placing a 0 cost card on the board - and at that, place it anywhere on the board so no one has the chance to counter you at all unless Tzeentch has a spare Changer of Ways or in the rare event all 18 card slots are filled.