Domain boundaries do not come from the org chart
A useful boundary surrounds decisions, language and rules that must remain consistent together. Splitting a system only by team or database table hides coupling instead of removing it.
Data ownership must be explicit
Define the source of truth, authority to change and publication mechanism for every entity. Copying data without a synchronization contract raises both change cost and inconsistency risk.
Integration is part of domain design
Versioned APIs, idempotent events, failure policy and observability should be designed with service boundaries so an internal change does not become a cascading failure.