There isn't an AoE spell that does exactly what you want but here's all I can think of that you can work with.
Spell Steal - Allows you to remove a single Positive Buff from an Enemy and apply it to a random ally unit OR removes a negative buff from an ally and applies it to a random enemy.
Dispel - AoE Dispels all buffs, negative and positive. Can also deal damage to summoned units in an Area.
Disenchant - AoE Dispels all buffs, negative and positive. Can also deal damage to summoned units in an Area.
Abolish Magic - Dispels all Positive Buffs from a target enemy or removes all Negative buffs from an Ally. Can also deal damage to a target summoned unit.
Devour Magic - Removes ALL buffs in an area and gives the caster mana and health for each buff devoured.
Purge - Removes all Buffs and can be changed to pause, or slow a target. Also deals damage to summoned units.
Channel - Can be made unit or point targetable, instant or channeled; you can then trigger the spell to remove positive buffs from enemies and negative from allies in an AoE.