While not related to the vetting of parties initially, this primary document gives some good insights to how the Communist Party of the Soviet Union responded well after the war with Warsaw Pact communist parties not aligning enough to the ideology the Soviet Union proclaimed. This led to the eventual invasion, occupation, and normalization of Czechoslovakia by Russian and Warsaw Pact forces, which involved all Warsaw Pact states, except Romania, attempting to reestablish socialism as envisioned by the Soviet Union.

Basically, they brought quite a few socialists and communists over to Moscow, particularly from Germany, in the 30s and through until the end of the war. They trained these people to be 'Moscow Communists' who were a world away from the views of many of the communist vote back in Europe. They then sent these men - providing they had not 'purged' them first - back to their home countries in the years following the war to take up high office, which surprised quite a few popular communists back home that had popular support locally and many of whom had worked hands on in resistance to the Nazis, rather than been holed up in Moscow fir the duration of the war.

Probably the most famous story is that of the Ulbricht Group which was made of up of German communists who had been staying at the Hotel Lux in Moscow, who were then quickly brought to Berlin to establish a Moscow friendly functioning administration, just as the NKVD had taught them to do.

For a more complete country by country explanation, check out Anne Applebaum - Iron Curtain.