The techniques described herein enable a commercial cellular service provider to use a repurposed portion of spectrum to provide cellular service to a customer base while ensuring that the use of the repurposed portion of spectrum does not interfere with a previous use of the repurposed portion of spectrum by an incumbent entity. The techniques determine, and manage the use of, forbidden cells and clean cells. A “forbidden” cell is a cell in which a previous use of spectrum by an incumbent entity is protected. A “clean” cell is a cell that can be freely used by the commercial cellular service provider without a possibility of interference with a protected use of the spectrum by the incumbent entity.