What does a spell blocked by might look/feel like?

Last session was the first time in my first ArM5 saga that a magus's spell has been blocked. A SG knight errant was over-excited, someone tried to cast a spell to calm his emotions, and the divine power of a holy relic worn by the knight prevented the spell from affecting him.

As I narrated the outcome, I realized that, while I clearly understood what happens if the spell penetrates, I didn't know what happens if it doesn't.

The spell would still be sucessfully cast even if it just had an individual target, I believe. Would the magus know that the target was not affected instantly, or would they have to wait and observe the target's emotions to know?

I'm sure this is right in front of me in the book somewhere, but I couldn't find it.

I think it is not defined. You can go for either. You can go for "I am massaging your mind Mr burns-style, and so know if I have touched it or not" or you can go for "I shot a cruiser missile and wait to see if I hit the target or not". We have used both. We even had an important guy in the local court that had a nice fairly powerful relic. He was a manipulative bastard that had Hermetic theory 3 and perception +3 as well as spies in the covenants of the tribunal to know what the magi could pull up, so quite frequently pretended to be under the effects of a Mentem spell when he was not. Made for a nice "this guy is good or bad or what? Ally enemy or just jackass??" confusing situation.