DDD Aggregates: Consistency Boundary - James Hickey
A consistency boundary helps us when we have business rules in our software that span multiple objects or have high contention. Let’s dig down a bit deeper!
  1. Define your invariants! What properties within your domain must always be true? Write these down somewhere.
  2. Invariants should then drive consistency boundaries.

If you are trying to split up consistency boundaries, invariants shouldn't straddle a consistency boundary!