property objects clean up

[Siqsuruq]

Hello,I've tried to ask a question in mailing list but it looks like its offline so I have a question about cleaning up property objects. Here is an example, class A has object bObj as property, when i destroy aObj, should bObj be destroyed too? Right?

package require nx

 nx::Class create A {
 :property {bObj:object,type=B,substdefault {[B new]}}

 :method init {} {
 }
 }

 nx::Class create B {
 :method init {} {
 :hello
 }

 :public method hello {} {
 puts "Hello from bObj: [current object] of [[current object] info class] class."
 }
 }

 # Create aObj
 set a [A new]
 # Checking instances of B
 puts "Instances of B class: [B info instances]"
 # Destroing aObj and check instances of B
 $a destroy
 puts "Instances of B class after aObj destroyed: [B info instances]"

Question number 2. When i do set :bObj [B new] old bObj should be replaced?

    package require nx

    nx::Class create A {
    :property {bObj:object,type=B,substdefault {[B new]}}

    :method init {} {
    set :bObj [B new]
    }
    }

    nx::Class create B {
    :method init {} {
    :hello
    }

    :public method hello {} {
    puts "Hello from bObj: [current object] of [[current object] info class] class."
    }
    }

    # Create aObj
    set a [A new]
    # Checking instances of B
    puts "Instances of B class: [B info instances]"
    # Destroing aObj and check instances of B
    $a destroy
    puts "Instances of B class after aObj destroyed: [B info instances]"

Or maybe I do smth wrong? What is the correct way to clean up after an object is destroyed? Even if I create a custom destroy method and do ${:bObj} destroy one of them will still be in memory. Thank you.