An apparatus and method are provided for managing a capability domain. The apparatus has processing circuitry for executing instructions, the processing circuitry when in a default state being arranged to operate in a capability domain comprising capabilities used to constrain operations performed by the processing circuitry when executing the instructions. A program counter capability storage element is also provided to store a program counter capability used by the processing circuitry to determine a program counter value. The program counter capability is arranged to identify a capability state for the processing circuitry. The processing circuitry is then arranged, when the capability state indicates the default state, to operate in the capability domain. However, when the capability state indicates the executive state, the processing circuitry is arranged to operate in a manner less constrained than when in the default state so as to allow modification of the capability domain. This provides a simple and effective mechanism for selectively allowing the apparatus to modify the capability domain.