  CrI$_3$ represents one of the most important van der Waals systems on the
route to understanding two-dimensional magnetic phenomena. Being arranged in a
specific layered structure it also provides a unique opportunity to investigate
structural transformations in dimension-confined systems. CrI$_3$ is dimorphic
and possesses a higher symmetry low-temperature phase, which is quite uncommon.
It contrasts with vanadium trihalides which show a higher symmetry
high-temperature. An explanation of this distinct behavior together with a
large cycle-dependent transition hysteresis is still an open question. Our
low-temperature X-ray diffraction study conducted on CrI$_3$ single crystals
complemented by magnetization and specific heat measurements was focused mainly
on specific features of the structural transition during cooling. Our results
manifest that the structural transition during cooling relates to the formation
of structural domains despite the lower symmetry structure transforming to a
higher symmetry one. We propose that these domains could control the transition
temperature and also the size of thermal hysteresis.
