These data centers are the sources and sinks for all kinds of abuse and attacks; have been for many years. The Russian government doesn't care what they go after as long as it's not in Russia, so the operations using these data centers operate with impunity.
Of course I've had most of them completely firewalled out for years, but every now and then one of them picks up an additional network block that's allocated elsewhere, the attacks start, and it's necessary to add that block to one of the existing rulesets. There are many sources for lists of Russian network blocks; one of them is
IPdeny country block downloads, which is updated quite often. (That link is for IPv4; note link on the page itself for IPv6.)
Note: it's advisable to make the firewall rules bidirectional. If you're defending a server environment, and nothing running there requires
outbound access to Russia, then make sure nothing has that access and make sure that you set alarms on any attempt -- because they may be an indication that you've been compromised and someone is trying to exfiltrate data. If you're defending a user environment, this is trickier -- on the one hand, none of your users should be accessing anything in the Russia, on the other hand they may get very upset when they find out they can't. But if -- for example -- your users are business users, and there's no business reason for anyone to reach Russian network space, then you can probably impose this as a matter of corporate policy. On the other hand, if your users are ISP clients, then you may not be able to make this stick.
None of this is a panacea. Proxies, VPNs, hosts in non-Russian clouds, compromised systems elsewhere in the world, all kinds of things combine to make this approach inadequate. But you should do it anyway, for two reasons: first, there's no point in making it easy for them. Second, if you don't perform this bit of due diligence, and things go sideways, you may be asked some very pointed questions about why you chose to skip something this obvious and easy.