There are arteries & veins in the neck around /under the scalenes & SCM, so be careful to not press on those areas. That's why it's best to learn from someone that can show you the safe places to press. Or study some anatomy books or websites.

TrPs
according to this chart the scalenes pain to these places -
http://www.pressurepointer.com/Scale...ger_points.htm
SCM would refer pain to theses places-
http://www.pressurepointer.com/SCM_trigger_points.htm

This might help you figure out if you might be pressing on a nerve and not a trigger point-
http://www.concordortho.com/patient-...a2995f76121bef