Church periodical teaches Flood was global cleansing of world.
"Concerning God's Justice and Mercy," The Latter-day Saints' Millennial Star 76, no. 8 (February 19, 1914): 121–122
The first example that naturally suggests itself to our minds, is connected with the deluge. At that time the whole world, with but few exceptions, had become so wicked that "It repented the Lord that he had made man on the earth, and it grieved him at his heart" (Gen. 6:6). The cause which gave rise to these thoughts is recorded in the preceding verse which reads, "And God saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually." When the Lord made known to Noah His purpose to bring destruction upon the antediluvian world, He said, "The end of all flesh is come before me; for the earth is filled with violence through them; and behold, I will destroy them with the earth" (Gen. 6:13). The wickedness which then prevailed among men was certainly of the most abominable character. Their deeds were corrupt. The earth was full of violence, and the thoughts of the people were of evil and of evil only. These conditions of wickedness provoked the Lord to the last degree, even beyond endurance. Never before nor since did He have such provocation for the display of world-wide, righteous anger and wrath as on that occasion. This is a point which should be kept constantly in view. But notwithstanding the greatness of the provocation, and in the midst of wrathful and well-nigh universal destruction, He did remember justice and mercy. Among the wicked multitudes there was a little company of righteous persons, and the eyes of the Lord were upon them always, and His protecting care was extended to them for their salvation. To destroy them was far from His thoughts: nor did he let the matter rest with this negative sort of interest in their welfare, as though allowing them a chance of escape, if they, themselves, could make provision for their own safety; but He took such a deep interest in their preservation that He gave Noah detailed instructions as to the means which lie should employ in order to put himself beyond the reach of danger. When Noah and his family had complied with these instructions, their lives were just as safe as though no flood had occurred. The ark of safety which had been built under the Lord's instructions was entered. They had entrusted their all to Him, and we shrink from the thought that He could betray them, either in the last or in the first stages of the event. Noah and his family were saved by the mercy of God, and by His personal efforts in their behalf.