Critical Mass noob question

Does Critical Mass apply raid wide?
For example if there are two fire mages in the raid, do each of them need to scorch so they get the 5% increase crit strike, or do just one of them need to do it?
The debuff is on the target, not on the mage. Every players attacking a target debuffed with Critical Mass will benefit from the 5% increased crit chance.
Makes sense. TY