Hi,
I had the same problem as shaman.
I´ve add these Spell ID to the Custom Debuff list 20604 "Dominate Mind".
And make a macro:
---
#showtooltip Purge
/stopcasting
/cast [@mouseover,exists,nodead][@target][@hbtarget] Purge
---
Than add the macro to the spell_list with the spell selector.
And its work. I purge two DDs last ID from Dominate Mind perfectly.