clean slate
A fresh start; another chance after wiping out old offenses or debts. This idiom often appears as wipe the slate clean. For example, Henry's boss assured him that the matter was finished and he could start with a clean slate, or He wished he could wipe the slate clean, but it was too late to salvage the relationship. This expression alludes to the slate boards on which school work or tavern bills were recorded in easily wiped-off chalk. Since 1850 or so the term has been used figuratively, and it has long outlived the practice of writing on slate.