While the Horus Heresy books have not got there yet is there any information as to what happened when Mars was re-liberated after the Horus Heresy? I am assuming it didn't take place until after the traitor legions had been pushed out of sol. Or is this whole civil war on Mars new canon that has not been mentioned before?
The civil war on mars was already canon, the imperium blockaded the planet during the horus heresy and were only able to retake it after the war ended. Exactly how is unknown although we can assume it was short and brutal.
Given that there were still quite a few primarchs hanging around on Terra and after securing the capital mars surely would have been the number one priority which probably received the tender attention of Dorn, Guilliman and the Khan.