Raincoat & Itching Powder

[Grej]

I have Raincoat, worn over another armor (e.g. Mithril Armor)
If Itching Powder makes me discard Mithril Armor, must I discard Raincoat too?

Raincoat card says, that it's going with another Armor, but Itching Powder says that I must discard one Item.