in Russia, besides the Bank of Russia there's also the National Wealth Fund (NWF), which is operated by the Ministry of Finance
in China, there's policy banks, such as China Development Bank which are supported by PBoC's facilities
this collateral (US Treasury bonds) can then be used on wholesale debt markets to issue more credit
moreover, this collateral can be leveraged/rehypothecated, thus increasing liquidity
still, in the USA the Fed continues to dominate in importance