I'm guessing you're talking about hit cap in relation to interrupting the adds in phase 2? If so, then you must've missed the part in the 4.1 patch notes that states that all interrupts that don't do damage will always hit, regardless of hit rating.
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All non-damaging interrupts off the global cooldown will now always hit the target. This includes Pummel, Kick, Mind Freeze, Rebuke, Skull Bash, Counterspell, Wind Shear, Solar Beam, Silencing Shot, and related player pet abilities.
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http://us.battle.net/wow/en/blog/2356431