When I was speaking to Asus about overclocking, they automatically assumed I had TM turned off, and told me to turn it off. Apparently it can interfere with overclocks, but I agree that it isn't well understood when it actually kicks in. Also I think secondary protections might be the motherboard 'Northboard' protection, it may save the motherboard if the cpu gets too hot, although I cannot say anything for the condition of the cpu.
Interesting that Asus assumed you had it disabled. That says a lot. Probably a good idea to just disable it as standard procedure for overclocking then.
I found this description of the TM function by the author of the i7 Turbo tool. As it's described here, it only takes effect when the CPU is on the turbo multiplier. So, for a 930, this would only occur if it's set to 22x, and the throttling would rapidly cycle it back and forth to 21x. And for the 920, it would occur at 21x and throttle back to 20x.
Reading more about thermal protection on core i7 systems, there are mechanisms provided by the board to automatically disable turbo mode if TDP limit or overcurrent condition occurs, and there is a thermal limit around 90C that will also disable turbo mode, and finally, a shutdown feature that will force shutdown at a little over 100C.