[development] Domain Access Cron

Anyone have experience with Domain Access and running cron? I'm setting up Domain access to work with multiple domains, all shared tables -- and I can't find documentation on how I should run cron. Should I setup cron to run on all domains or just on the "primary" domain? I'm sure the answer is that it depends. I'm sure this is obvious to some, but I'm worried I'll make a fatal mistake. Josh