when the reflex action has been performed,how the message about that action reaches the brain later on?

Action potentials.

when the reflex action has been performed,how the message about that action reaches the brain later on?

 

Well it doesn't - that is the point of a reflex.

 

Although sensory impulses from the limb doing the reflex action would reach the brain hence you are aware of the sensation of your limb moving.

Reflexes are the automatic reactions of the nervous system to stimuli impinging on the body or arising within it. The message about any movement in the reflex action reaches through reflex arc. By following a reflex arc, nerve impulses travel along sensory neurons from the site of stimulation to the spinal cord or brain and then back to the area of the response along motor neurons.