There were two different tier sets for priest, one for healing and one for DPS.
Tier 6 tokens dropped of bosses in three different raids. There were eight pieces in this tier.
Gloves token – Azgalor in Hyjal Summit
Helm token – Archimonde in Hyjal Summit
Shoulder token – Mother Shahraz in Black Temple
Pants token – Illidari Council in Black Temple
Chest token – Illidan Stormrage in Black Temple
Bracers token – Kalecgos & the Eredar Twins in Sunwell Plateau
Belt token – Brutallus & the Eredar Twins in Sunwell Plateau
Boots token – Felmyst & the Eredar Twins in Sunwell Plateau