Where to place POCOs validation - N-layers arquitecture

I am developing a n-layer app. One of the layer is the BusinessLayer and consumes a set of POCOs defined in the CoreLayer

CoreLayer

• POCOs (classes with properties)

• Repository interfaces (use the POCOs as parameters types) For example :

  public interfaces ICarRepository { IEnumerable<CarPOCO> GetAllCars(); }

  public class CarPOCO { public int Id{get;set;} public string Name{get;set;} }

BusinessLayer:

• Businnes logic
• I want to put here the validation of the POCOs data, but i am not sure if is the right place, or how to deal with it

What do you think? How you will do that?

Many thanks, you are awesome.