Using any brush or cloth might leave scratches on the strike, I have found two things that wok well, the first is a solution called eZest Coin Cleaner (also know as Jewel Luster) and can be bought online, you just dip the entire strike in for a second or less and rinse right away with water and pat dry with a soft cloth, the second thing I have used is good old Ketchup, rubbing it on with my finger and rinsing off with warm water. I like the eZest best.
Again Never use a brush or cleaning cloth if you care about not scratching your strike.
Walt