Yup, got it.

so knockback damage is treated as adding to the regular damage in the attack?

where in the rules is this treated?

wouldn't Invulnerability subtract 2 from the regular damage and then also subtract 2 from knockback damage?

from the rulebook:

No, Invulnerability/Toughness is 'reset' every time the dice are rolled (there are exceptions).

The only time you'd see Invulnerability/Toughness soak knockback damage would be when Psychic Blast is used in the attack.

i see....so why does it say that in the rules?

...from the FAQ.

This says that a dice roll is SUFFICIENT to reset toughness, but not NECESSARY.

It doesn't say,

"a dice roll is made to hit the character with Toughness if and only if it “resets” and stops another 1 point of damage."

what i'm trying to say is that it seems like it says that a die roll is not the only thing that will reset toughness

Also toughness and invulnerability would absorb knockback damage from force blast, though impervious will not.