It's still a bit confusing because the USSR had several names for each, but...

Mars 2 crashed on Mars 1971
Mars 3 soft landed but stop working after ~90 seconds 1971
Mars 6 crashed on Mars 1974

As far as I know non of these Soviet Landers went thru any sterilization of anykind...

Here is part of an article from a few years ago at Spacedaily.com:

***The U.S. isn't the only country to send probes to Mars and the other planets. The former Soviet Union and Russia have sent several probes to the red planet. Some were successful, some not. There is no way to confirm that the Russian probes went through any sort of decontamination before launch.

"Although the Russians were saying they want to do that, that they intend to do that, and it's their policy to do that - its never really been documented what was done," Rummel says, referring to Russian decontamination policy. "Everything we understand about the way they process payloads would suggest that it would have been very difficult for them to actually have launched the spacecraft that was clean, even if it was cleaned before launch."

As an example, Rummel points to the saga of the 1988 Phobos spacecraft. "I do know that the Phobos launch vehicle was in a room with a bunch of people having a reception before it [was] launched. It's the sort of thing that one wonders whether or not … everything that could have possibly been done for contamination control [had] been done at that point."***