Many good Bible teachers and scholars do take the view that the reference to “angels who did not keep their own domain” is a reference to that group of fallen angels whom Satan persuaded to cohabit with women (Gen. 6:1-4) and who were confined immediately because of the gross nature of that sin. The apocryphal book of Enoch describes their dramatic end. Another passage that may apply here is 2 Pet. 2:4-5 which says “For if God did not spare angels when they sinned, but cast them into hell and committed them to pits of darkness, reserved for judgment; and did not spare the ancient world, but preserved Noah, a preacher of righteousness, with seven others, when He brought a flood upon the world of the ungodly.” Some believe these are the fallen angels who sinned grievously by cohabiting with women, as described in Gen. 6:1-4 (see Jude 6). Or this may refer to angels who rebelled with Satan before Adam and Eve sinned. In either case they were consigned to hell, lit., tartarus, a prison holding them until their final judgment. Some evil angels, the demons, are still free and doing Satan’s will. The logic is that if God so punishes angels, surely He will not spare these false teachers.
For more detail on this, see Bob Deffinbaugh’s excellent study on Genesis 6 on our web site. I personally think this is what Jude, 1 Peter 2:4 and Gen. 6 are talking about, though other Bible teachers disagree.