Domestication's triggered ability has an "intervening 'if' clause." That means (1) the ability triggers only if the enchanted creature's power is 4 or greater as your end step begins, and (2) the ability does nothing if the enchanted creature's power is 3 or less by the time it resolves.

Domestication can target, and can enchant, a creature with power 4 or greater. The enchanted creature's power is checked only when the triggered ability triggers and resolves.

If an effect changes the enchanted creature's power until end of turn, it will still have the modified power during your end step.