One cell, one owner
A domain cell groups the data, rules and interface for a single area of accountability, onboarding, claims, reconciliation. Because one person owns the outcome, decisions about the cell can be made without convening the whole organization.
Explicit contracts between cells
Cells exchange defined messages rather than reaching into each other's storage. The contract states the fields, the guarantees and the failure behaviour, which is what allows one cell to be rebuilt while the others keep running.
Size the cell to the change rate
Areas that change often deserve smaller, more isolated cells. Stable areas can be larger. Matching the boundary to the expected rate of change keeps future work proportionate to the business need.