The THAI Spa is airside international. So, no, you can't get a free 30 min massage when flying domestically.
In fact, on the domestic side, I can't recall if there are any options for a 'paid massage' once you have moved through to Concourse A (level 4). However I think there is something on Level 3 landside amongst all the Starbucks and other little restaurants - but I can't be sure.