Jeez! Six or seven times and you were still gutsy enough to get back on that bike? Wow, I am so glad you were not seriously injured. That could easily have been a disaster for you.

I had these high speed wobbles two or three times on different bikes. Scary as hell but I was lucky to never go down.

High speed wobble can be caused by so many things; fork, headset, wheel bearings, spokes, wind, speed, road surface, etc... and any combination of those and other things.

The Trek Domane has yet another set of considerations that have been hinted at but (unless I missed it) have not been specifically mentioned; the IsoSpeed decouplers. Never ridden with them, and I'm sure Trek researched the hell out of the design and implementation. But aren't the ones on the Sl6 adjustable? Is there some possibility that the ones on this particular bike are a little off?