The Prophet's Heart Washed

Jubril did the exact same thing that he opened up the chest of the Prophet ﷺ before taking him on the journey and he washed it in zam zamwadir. There was no black cloth the second time because the black cloth has already been gotten rid of when the Prophet is four years old. The spiritual benefits that we derive from this particular incident is that the Prophet  is being prepared for a pure and clean life. Allah doesn't need to leave a scar because Allah heals and complete but Allah wants to demonstrate that something physical happened.