My other 2 tanks (BrM/BDK) has no issues dealing with it since they have a great AoE snare, but I have trouble dealing with it on my VDH.
A lot of people recommend getting Razor Spikes talent, but it looks pretty useless. It only procs from your melee damage and pretty much the only time I have a problem with Necrotic is when there are 5+ adds stacking it up on me quickly. You just don't don't have time to tab target through them all to snare them.
The only real ability we have to deal with it is Sigil of Chains which is an AoE 70% snare and lets use get away, but it's on a 1.5m CD. For places like Nelth or Lower Kara where every other pull is a pack of 5+ mobs, it's not that great.
The real only surefire way I could deal with it is by relying on a Shaman/Mage/Fury/etc to use their AoE snare before I kite or by not running those dungeons at all, which I think is pretty lame.