You can’t go wrong in assuming it is corrosive. I had, and shot, some Indian 7.62x51mm which was marked as being NATO M80, and I was almost certain it had to be non-corrosive, as it was headstamped as being made in the 1980s, and put off cleaning until the next day. Sure enough, the next day I had a coating of light rust in my bore. I managed to get most of the rust out with a lot of elbow grease, but the bore is still slightly dark (this was a pre-64 Winchester Model 70 in .308).
I ALWAYS use hot water to clean my bores if I shoot corrosive ammo. Don’t assume any commercial bore cleaner will do the job. The issue bore cleaner used by the US Army back in the WWII-Korea era was supposed to do a good job of removing corrosive primer residue, as it contained some water to dissolve the chloride salts. After you pour water through the bore (or use water-wet patches if you can’t pour water), dry the bore thoroughly using dry patches and follow up by using Hoppe’s, Birchwood Casey, Shooters’ Choice, or whatever bore cleaner you normally use.
Another caution - If you intend to reload cases that were originally primed with corrosive primers, be sure to wash the interiors thoroughly with hot water before loading them.