monsterer is wrong again. Even within the block there is no way to attain commutativity of ordering. Any particular choice of arbitrary orderings of script executions for a block result may achieve a different result for contracts than another ordering (unless the scripts are invariant to ordering but that basically means the scripts can do nothing). That is the definition of indeterminism.
Perhaps I should have said 'within one script execution within one block'. Block ordering is eventual, just like bitcoin. In ethereum this has scope for more dire consequences than it does with bitcoin; it depends on the application.