The only formal structure in place in respect of transfers at Executive Officer level and above is the Central Applications Facility (CAF) that was established for locations included in the Decentralisation Programme. The CAF is administered by the Public Appointments Service.
While my department maintains informal transfer lists for the grades of Executive Officer and above I understand that not all departments do so. If an individual serving in my department wishes to be considered for a transfer to a department or location other than a CAF location, it is open to them to specify the Department or locations which are of interest to them to the HR Division of my department. HR in turn will forward the details to the relevant department asking that the person be included on the transfer list where one is maintained.