Monitoring control for multi-domain processors

There is provided a method of controlling a monitoring function of a processor, the processor being operable in at least two domains, comprising a first domain and a second domain, the first and second domains each comprising at least one mode, the method comprising the steps of: setting at least one control value, the at least one control value relating to a condition and being indicative of whether the monitoring function is allowable in the first domain; and only allowing initiation of the monitoring function in the first domain when the condition is present if its related control value indicates that the monitoring function is allowable. In some embodiments the first domain is a secure domain and the monitoring function is a debug or trace function.