Maybe the first time I've posted my question in the wrong section: maybe I'll get a better luck asking here. Maybe.

Well, are AMD (as well as Intel, of course) CPUs supposed to scale down their cores' clock frequency/multipliers, when any overheating occurs?

In case, is there any setting, method, technique, or software able to show those throttling occurrences in any case?

The question may look rather obvious, but seemingly I'm not able to actually detect any change in cores clock frequency (I've used AMD OverDrive 4.2.1, CPU-Z 1.57, RMClock 2.3.5 and Throttle Watch 2.02), expectedly due to thermal throttle (currently on three AMD 10h CPUs, Phenom II X4 980, Athlon II X4 605e, Athlon II X3 420e), up to 117° C reported core temps (I used two more tools, Core Temp and SpeedFan).

I was also unable to detect any sudden deep dip in the temperature graphs (on SpeedFan), which would have been able to reveal a drop in clock frequency, as some one has suggested to me.

Hmm, this doesn't quite answer your question, but can you test using Realtemp? When you launch the main program, it will show the thermal status at the bottom. If the cores have overheated, it will show "LOG" on the thermal status. Don't know if that means that the cores have throttled back, though, just that the thermal monitor has tripped...

quest_for_silence sent me a PM so Im going to answer in spite of my cluelessness...

I've never trusted thermal throttling before.
In situations with poor cooling, I've either underclocked through the BIOS or dynamically in software.
Maybe thermal throttling has worked for me before but either it was transparent or I wasn't looking.

I do not know which CPUs automatically throttle when they get hot. I vaguely reacall hearing that some Intels disable their turbo if they get too hot or something. But I assume that if AMDs do have thermal throttling, it's either only specific models or only the newest models which have it.
And assuming one of your CPUs has this feature, you'd need to know how it works do detect it: maybe the throttling doesn't use the temperature which is reported to you but another feedback. And does it merely prevent overclocking or actually turn the clock lower than the nominal frequency? Furthermore, can the motherboard override the automatic throttling? Maybe you need to change BIOS setting to allow it to work.
In short, if you know as little as I do about this, step 1 would be to get more information about this stuff. The most obvious way to do that would be to read AMD's documentation and/or to ask them directly. You could also look at newsgroups, mailing-lists and forums dedicated to AMD's CPUs. Failing that, I guess you could try to ask kernel hackers on IRC or others who routinely deal with all sorts of hardware issues.