Apex domains cannot have CNAME records.
Question and response
Question
dig salesforce.com. NS
Answer
salesforce.com. 5 NS udns1.salesforce.com.
salesforce.com. 5 NS pch1.salesforce-dns.com.
salesforce.com. 5 NS udns3.salesforce.com.
salesforce.com. 5 NS udns4.salesforce.com.
salesforce.com. 5 NS pch2.salesforce-dns.com.
salesforce.com. 5 NS udns2.salesforce.com.
Authority
The response has no authority records.
Additional
udns1.salesforce.com. 5 A 156.154.100.8
udns2.salesforce.com. 5 A 156.154.101.8
udns3.salesforce.com. 5 A 156.154.102.8
udns4.salesforce.com. 5 A 156.154.103.8
udns1.salesforce.com. 5 AAAA 2001:502:2eda:0:0:0:0:8
udns2.salesforce.com. 5 AAAA 2001:502:ad09:0:0:0:0:8
udns3.salesforce.com. 5 AAAA 2610:a1:1009:0:0:0:0:8
udns4.salesforce.com. 5 AAAA 2610:a1:1010:0:0:0:0:8
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0