As I understand, in most economies, the central bank is supposed to be in charge of monetary policy, which in part means that they are supposed to be the only authority which can increase the amount of currency units available in the economy.
With physical currency, this can be done by making sure that the central bank is the only entity which has access to a mechanism that prints paper notes. Then, the only thing that other banks can do is manage reserves of such paper notes that their clients have given them.
However, if I understand correctly, many modern economies are based on electronic accounts rather than specific physical goods. This means the banks basically have a table which associates each account with how much money it has, and most transactions are only manipulations on these tables.
In such a situation, how can the central bank make sure that the total amount of currency in the economy (i.e, the sum of the values in all the entries of all tables in all banks) is not changed without their permission?
For example, let's say that Bob has 100 units of currency in a non-central bank B. What prevents the bank from changing that number from 100 to 101 in their internal records? I can see that this bank will run into problems if Bob wants to transfer their funds to some account in a different non-central bank C. However, it is not too hard to imagine a situation where such a situation would be unlikely: for example, consider a non-central bank in a remote village where all villagers keep their money in that bank.
So, in an economy not based on physical assets, but electronic accounts, how do central banks force their monetary policy onto non-central banks?