MySql Replication Failure on primary secondary
In the master server, you don't need to issue either RESET MASTER nor PURGE BINARY LOGS to extract a DB copy... when you need to extract a master copy to create a slave, just do it with the current binary log file and position.

Since you will need the current binary log file and position to start replication on the slave, just include the --master-data (more info) option to mysqldump which automatically appends the CHANGE MASTER TO statement required on the slave to start the replication process.
(Just open the mydb-dump.sql file after backup is completed and copy the "CHANGE MASTER TO" info.

In slave is perfectly safe to use RESET SLAVE after a backup restoration to start the replication.