The components section for forbiddance says:
V, S, M (a sprinkling of holy water, rare incense, and powdered ruby worth at least 1,000 gp)
This does not explicitly state that the spell consumes them, which is the norm for spells that consume their material components.
However, the spell also states:
If you cast forbiddance every day for 30 days in the same location, the spell lasts until it is dispelled, and the material components are consumed on the last casting.
This got me wondering if this means the material components are only consumed at the end of a 30-day casting, or whenever you do not cast the spell in the same place the day after casting it last?