This issue is about creating an enhancement for Dispeller addon. The addon needs to identify buffs that can't be dispelled by normal dispelling abilities (e.g Purge, Dispel Magic, Spellsteal), and suggest an alternative skill.

Examples:

• The only abilities in the game that can dispel Divine Shield are the Priest's [Mass Dispel] and the Warrior's [Shattering Throw].
• Ice Block can be removed via [Mass Dispel], and in rare cases [Purge] and [Dispel Magic] only if these spells are cast at the same time as Ice Block.

Keep in mind this comment from wowhead:

You can, to an extent, control who you can include in your Mass Dispel. Targets that are closest to the center of your casting circle (where you clicked) will have a higher priority than those that are farther. These include, but may not be limited to, pets and friendly NPCs.

Mass Dispel DOES NOT differentiate whether the person has a debuff or not. If someone has no debuff, they will "take up" a dispel if they are closer to the center.