Why is FAC 1 cycled OFF to ON during a dual engine failure?
Resetting FAC 1 enables the recovery of characteristics speed displayed on the PFD.
  Resetting FAC 1 also enables rudder trim recovery, even if no indication is available.
  When the hydraulic power is lost, the right aileron is lost, and is in the upfloat position.
  Rudder trim may be used to compensate for this upfloating aileron.
  


This is from the QRH under 'ENG DUAL FAILURE'. That answers why FAC 1 is reset.

FAC 2 on the other hand (unlike FAC 1) is not powered by the emergency electric system, see § Flight Control System - Electrical Supply. And that's why you don't cycle FAC 2.

From the same section FAC 1 is not on a hot (stand by) supply, so after a power interruption it requires a reboot (my interpretation).


(Red highlight mine)



Do not use for flight.