Characters gaining a temporary resistance to magic after being affected by a scroll would seem like a reasonable mechanic.
That was exactly what I was just thinking.
A strong resistance to magic immediately following, that slowly decays over the course of 2 weeks or so. Possibly even not decaying at all if the affected character is wounded, so as to avoid situations where you're wounded for exactly as long as you have magic resistance.
It shouldn't be too difficult to implement, either.
