The only spacecraft that I'm aware of that were fully sterilized were the Viking 1 and Viking 2 landers. They went through dry heat microbial reduction.
That page notes that some parts of the Beagle 2 lander were sterilized.
The MSL (Curiosity) drill bits and other components were sterilized, though the drill bits were later exposed to a clean-room environment without being re-sterilized. That turned out to be ok though, due to the nature of the selected landing site.
All other US Mars landers were simply cleaned and assayed to verify the bioburden limits (which are not zero).
Parts of the early Rangers (1-5) were sterilized and had gaseous treatments. They all failed, blamed in part on those processes. The direction was changed in 1962 to not apply either dry heat or gaseous sterilization to lunar probes.
It is difficult to know what exactly the Soviets did to Moon and Mars vehicles. This book describes some attempts to find out.
Gause assured Sagan that mission staff had sterilized Luna II’s
instrument package and its third stage carrier rocket, both of which
had impacted the Moon. But when pressed for details, Gause said some
curious things, claiming “that his knowledge of the sterilization did
not exceed that published in Izvestia." He said that the sterilization
methods were those known to every graduate student in microbiology at
the University of Chicago, and to every manufacturer of canned food,
but he would not be more specific than that.
For Soviet Mars spacecraft:
Vashkov claimed that individual parts of landers were sterilized by
heat (although he did not give the temperature or duration of the
procedure) or by a radiation dose of
2.5 millirads, depending on the characteristics of the part. The landers were assembled in cleanrooms, and individual parts were
carefully cleaned, probably with hydrogen peroxide. UV light was
applied during assembly as an additional sterilant. Finally, before
launch, Soviet mission personnel exposed the entire lander to a methyl
bromide–ethylene oxide gas mixture for 6 hours at 50°C.