The chromatin which permanently remains in the heterochromatic region is

The chromatin which permanently remains in the heterochromatic region is Constitutive heterochromatin.
Constitutive heterochromatin domains are regions of DNA found throughout the chromosomes of eukaryotes.
The majority of constitutive heterochromatin is found in the pericentromeric regions of chromosomes but is also found at the telomeres and throughout the chromosomes.